The present invention relates to the field of enclosures for electrical or electronic equipment in general and to the electromagnetic sealing of such enclosures in particular.
Enclosures, both conductive (e.g. metal) and non-conductive (e.g. plastic) are used to house electrical and electronic equipment. Where electromagnetic compatibility (EMC) is a problem, e.g. either in the form of electromagnetic interference (EMI) from outside the enclosure affecting sensitive apparatus inside, or vice versa, measures are taken to make the enclosure an effective electromagnetic (EM) screen.
Metal enclosures are obviously to be preferred from an EMC point of view, although cost, aesthetic and other factors mean that plastic enclosures are often used. In order to offer EM screening, plastic enclosures are coated with a conductive skin (e.g. metallic paint) or, alternatively, conductive, metal loaded plastic may be used. These enclosures are typically assembled from two matching halves mated together. Despite the use of conductive materials, EM leakage may occur at the join between the two halves. A known method to reduce EM leakage at the join is to insert a soft, metalised gasket along the join. A complementary measure is to include frequent fixing points (i.e. for fixing the two halves together) around the enclosure in the vicinity of the join to counteract the tendency of the join to open at sections away from the fixing points.
The introduction of extra fixing points leads to increased complexity of the mould or the machining and increased assembly time. The use of gaskets increases cost and assembly time.
Another means to improve EM screening is to create a tongue and groove joint between the two halves. A continuous groove is moulded or machined into the mating surface of one half of the enclosure and a complementary tongue (or wall) is moulded or machined on the corresponding mating surface of the other half. Disassembly is a particular problem where metallic coatings such as metallic paint are applied to the tongue and groove. In order to ensure ease of disassembly, the fit between the tongue and groove is designed to be generous.
However, this generous fit leads to poor electrical contact being obtained between the mating surfaces resulting in gaps in the EM seal which allow the passage of unwanted EM radiation.
Use of the present invention provides good EM sealing of enclosures with low cost and easy assembly.
The present invention provides an enclosure for electrical or electronic equipment comprising a first and a second electrically conductive body part, the first and second body parts each comprising a mating surface for mating with the mating surface of the other body part on assembly in which at least one of the mating surfaces comprises a plurality of electrically conductive projections for contacting the other mating surface when assembled; in which the mating surfaces are disposed at the periphery of the relevant body part, in which the plurality of projections are dispersed along the periphery, and in which each projection is substantially electro-magnetically shielded by at least one of the body parts when assembled; in which the electromagnetic shielding comprises portions of the first and second body parts which overlap each other when assembled; in which the electromagnetic shielding comprises a tongue on one mating surface and a groove on the other mating surface.
In a further preferred embodiment the invention provides an enclosure comprising a panel groove for mounting a panel, in which the panel groove comprises one or more electrically conductive projections on the groove surface for contacting the panel when assembled.